Where there is a need to position and remotely control machinery with a high degree of precision, robots are often used to perform these tasks. Robots in the past have been utilized to perform both simple and complex tasks in various environments, particularly where human activity is inaccessible, prohibited or relatively hazardous. More recently robotic type apparatus has been put to use in outer space. Typically where such robots are used, either tools or end-effectors are attached to movable robot arms so that objects can be grasped, lifted, manipulated and otherwise operated upon.
One known type of end-effector comprises a gripper comprised of two mutually opposing jaws that are movable with respect to one another in opposite directions by a rack and pinion gear mechanism. Such apparatus is shown, for example, in U.S. Pat. No. 4,707,013 issued to John Vranish et al on Nov. 17, 1987, and which is herein meant to be incorporated by reference. There the gripper includes a pair of rails having parallel thrown motion with a gripper finger sub-assembly attached to opposite ends of each rail. A pair of preloaded linear bearings engage the outward surfaces of each rail and two roller bearings spaced on either side of a pinion, all mounted on a common pinion shaft, engage the inward sidewalls of each rail. The rails are typically driven by an electric motor.
Further, the gripper design as disclosed in U.S. Pat. No. 4,707,013 incorporates separate racks that need to be first fabricated and then bolted to the rails, increasing the weight and bulk and making it relatively complicated to assemble. In order to achieve sufficient strength in the pinion shaft bearing, moreover, the back of the gripper housing protrudes significantly, further adding to the weight and bulk of the gripper. Also, when the fingers experience a sideload, the rails tend to move sideways relative to one another. Because the ends of the other sides of the rails are fixed, it has the effect of spreading the housing, eventually bending it open, causing preload on the bearings to be lost.
Strain gauges are also mounted on the fingers to sense gripper pressure, with service loops connecting to the gripper base. The service loops being subject to many cycles of flexing, have a tendency to snag on other parts of the gripper. Moreover, finger mounted strain gauges are easily damaged, if the part being gripped is inadvertently gripped on the finger shanks. Furthermore, strain gauges require individual calibration for each set of fingers to obtain reliable readings since each mounting situation is relatively different and the fingers vary slightly from element to element. Also, finger mounted strain gauges are sensitive to loads other than the finger grip force such as sideloads.
It should also be noted that rotary tools, particularly those mounted on robot end-effectors, are generally not retractable and fully protrude into the work space and as a result, generally require an actuator to release them.